Electron gun for electron tubes in cathode heater device



Oct. 21, 1969 H. K Tz ETAL 3,474,282

ELECTRON GUN FOR ELECTRON TUBES IN CATHODB HEATER DEVICE Filed June 27. 1966 IINVENTORS HELMUT KATZ PAUL MEYERER BY ATTORNEYS United States Patent 3,474,282 ELECTRON GUN FOR ELECTRON TUBES IN CATHODE HEATER DEVICE Helmut Katz, Munich, and Paul Meyerer, Ottobrunn,

Germany, assignors to Siemens Aktiengesellschaft, a corporation of Germany Filed June 27, 1966, Ser. No. 560,423 Claims priority application (figrmany, June 30, 1965,

Int. Cl. H01j 1/14, 19/06; H0lk 1/04 US. Cl. 313-346 7 Claims ABSTRACT OF THE DISCLOSURE support it and extending toward the auxiliary cathode,

and an additional foil cylinder of molybdenum mounted within the tantalum foil cylinder and formed with a plurality of apertures for focusing the electron beam from the auxiliary cathode and the emission from the auxiliary cathode impinging upon the main cathode to heat it by electron bombardment.

The invention is directed to a beam production system for electrical discharge vessels, in particular power tubes, in which system the cathode emitting the beam electrons (beam system cathode) simultaneously forms an operating electrode of an auxiliary electron discharge system, serving for heating by electron impact.

It is of particular importance in high power tubes such as traveling wave tubes operating with electron beams, in which type of tubes, required for the beam formation and those disposed directly adjacent to the cathode, sufficiently cool so that, even when emission-promoting substances are vaporized upon them, they do not supply any thermic emission. Such cooling requires measures to assure that the amount of heat emitted by the cathode, is reduced to as small a quantity as possible. At a predetermined cathode temperature the amount of emitted heat absorbed by the adjacent control electrode depends upon the size of the surface of the particular cathode in view of the ensuing heat emission and upon the heat conduction due to the required mechanical connections for support of the elements.

However, with the requirements regardless the specific emission of a cathode, to be expected at the present and, more particularly, in the future, the cathode temperature :must be increased to over 1100. The customary method for heating a cathode utilizes a heater which, by passage of electrical current, produces the necessary heat. Certain requirements, however, must be made with respect to the heater. If it is located in the immediate proximity of the cathode surface, it should, if possible, not produce an alternating magnetic field and, thereby, a hum. The current conduction therefore should, it possible, be bifilar and the heat current intensity should appropriately be kept as low as possible. While a heater made of suitably thin wire, meeting these requirements, has a small heat dissipation, as a result of its insufiicient rigidity in correspondence to its low mechanical stability, it cannot be suitably constructed and arranged to achieve a long useful life without adequate external support. It is, therefore, necessary to insulate it in connection with such support, the insulation being in contact with the true cathode so that it has to withstand a certain electrical voltage between heater and cathode. The quality of this insulation depends, among other factors, upon the height of the heating temperature. In order to keep this temperature as low as possible, frequently the entire inner space of the cathode is filled with insulation material, i.e., the heater spirals are cemented into the heater space in order to direct the heat to the actual cathode by means of the heat conduction of the insulation material involved, even at relatively low heater temperature. This type of heater construction has the advantage that it results in a relatively small heat loss. However, for the accommodation of the heater, a considerable space is required which corresponds to a cathode body of much larger dimensions than that actually required for the desired emission. The heat to be produced therefore amounts to a multiple of the quantity of heat actually required for the emission, so that an unnecessarily high amount of heat is received by the initial electrodes. In addition to this, the problem of the insulation also begins to become critical for this so-called cemented-in heater. The occurrence of electrolysis within the insulation material, just to mention one of the possible disturbance symptoms, depends upon the temperature, not directly, but exponentially so that a necessary cathode temperature increase of only 20 may operate very disadvantageously in such a way that, for example, the insulation cannot be accurately controlled to provide a guaranteed long life.

It is, therefore, the purpose of the invention to achieve, by special constructional features, a beam system cathode in which the size and thus the surface thereof is as small as possible and, at the same time, to simultaneously avoid the previously described disadvantages of the prior customary constructions of such systems, in order to keep the temperature of the standard beam-forming electrode, immediately surrounding the beam cathode, as cool as possible so that such electrode cannot cause any thermonic emission during operation, even if emission-promoting substances are vaporized thereon.

The term metal capillary cathode as used herein means an indirectly heated dispenser cathode in which an emission promoting substance such as barium, is contained in a supply chamber that is covered by a porous emission material carrier or in the pores of this carrier, i.e., a plate whose structure remains porous in operation, for example, a plate of refractory metal such as tungsten, in particular, a porous sintered tungsten, and the emission promoting substance liberated, i.e., in the supply chamber passing only by means of diffusion along the porous walls to the emission surface, so that it is uniformly distributed over that surface during operation. For a more detailed explanation of metal capillary cathodes, an article entitled Metal Capillary Cathodes, which appeared in the Journal of Applied Physics, vol. 24, No. 5, pp. 597-603, May 1953, may be consulted. In a beam production system for electrical discharge vessels according to the invention, as initially described, this is obtained by the feature that, for the emission of the beam electrons, a storage cathode, in particular an MK-cathode, with a frontal porous carrier disk for the emission material of large diameter is provided, which may be impregnated, and which closes a relatively shallow storage container of cylindrical shape, filled with a supply substance, the bottom of which container represents the actual electron impact plane of the operating electrode of an auxiliary electron discharge system, axially arranged at the adjacent side of said cathode, i.e., the opposite side thereof with respect to the direction of the cathode beam emission.

In this arrangement, the beam emission cathode is constructed without a heater and consists, therefore, only of the carrier disk for the emission material, forming the emission surface, and the emission material supply container which is covered by such disk, said container to receive its required heat supply, as an operative electrode, by electron impact from an auxiliary discharge system. Because of this, the dimension of the actual cathode can be kept very small so that the heat produced closely adjacent to the heat-critical electrode can, as a result, likewise advantageously be kept to an especially small amount.

Advantageously, the required cathode, necessary for the auxiliary discharge, is likewise constructed as a storage cathode, of generally much smaller construction, in particular as a metal capillary cathode, which also has a frontal emission material'carrier and for the heating of which an appropriate customary heater is provided. However, as this heater is located much further away from the heat-critical electrode involved, its heat effect thereon is negligible. For an effective shielding of the discharge of the auxiliary system with respect to the principal system, a tube-shaped accelerating anode for the auxiliary system, provided with one or several diaphrgms is arranged coaxially in a heat protective shell, constructed as a tantalum foil cylinder, and serving as the support for the principal cathode. In especially advantageous manner, at least one of these diaphragms is proprovided with getter metal, for example zirconium, and its opening is so proportioned that it receives sufiicient heating by impact from the auxiliary electron discharge. Due to the fact that the auxiliary discharge takes place with relatively high current density, it has at the same time, at least partially, the function of an ionization zone so that, in connection with the aperture diaphragm, which is capable of gettering, an effective ion gettering pump is formed. In an advantageous development of the beam production system, the thermo-voltage, which is produced, during operation, at the junction formed by the cathode carrier, consisting of molybdenum, and the tantalum foil cylinder, is conducted to the Wehnelt-electrode, directly or appropriately amplified, for control of the intensity of the discharge current, and thereby so controlling the emission temperature of the principal cathode that, for example, an automatically operating temperature regulation is obtained.

More detailed features of the invention are explained by means of the example of construction of a beam production system, shown purely schematically in the figure of the drawing, in which parts which do not necessarily contribute in longitudinal section to the understanding of the invention, have been omitted or not marked.

-In the figure, the heat-critical beam-forming electrode of the beam-production system is designated by the reference numeral 1, with the beam system cathode 2, 3

being constructed as a storage cathode, in particular as an MK-cathode, which is located in the diaphragm opening of said electrode. The cathode consists of an emission material carrier disk 2, forming the emission surface, and a storage container 3, which is covered by said disk. It has no customary heater so that its cathode body, the storage container, may be constructed as a very flat cylinder. Because of this construction, its surface is kept very small so that at this point the heat transfer, important with respect to the beam-forming elecrode, is at a minimum. The cathode carrier is supported by a beam protective shell or housing comprising a tantalum foil cylinder 4 which is attached to cathode body 3 directly below the emission material carrier disk 2 and may be surrounded by still another beam protection cylinder 11. The heat supply is achieved by electron impact from an auxiliary electron discharge which is produced substantially within the beam-protection case 4 by means of a coaxially disposed auxiliary discharge system. For this purpose a tubular-shaped accelerating anode 5, provided with one or several diaphragms 6, 7,

is coaxially disposed inside the beam protection cylinder 4. Positioned in front of such anode is an auxiliary cathode 8, constructed as a storage cathode, in particular, as an MK-cathode, having a heater 9 and appropriate Wehnelt cylinder electrode 10.

During operation of the disclosed beam-production system, an electron fiow initially takes place from the heated cathode 8, said flow being accelerated through the anode 5 with its diaphragms 6 and 7 towards the principal cathode 2, 3 and flowing with a relatively high discharge density. One diaphragm, in particular the diaphragm 7 arranged on the inside of the tube-shaped electrode, is covered with a metal capable of gettering, for example with zirconium, titanium or the like, as a result of which the remaining gases ionized in the discharge interval can be gettered by such diaphragm. For this purpose, the diaphragm opening is so selected that it is smaller than that of the entrance diaphragm whereby a heating, sutficient for the gettering process, takes place due to the electron impact occurring in a manner similar to that of an aperture diaphragm. It is included in the method according to the invention to direct and control the discharge in such a way, when placing the discharge vessel involved in operation, that a sufficient pump effect is obtained without a considerable heating of the beam cathode. Naturally, a pump effect providing a high, good vacuum can be obtained continuously during operation of such an emitting principal cathode by means of the ionization source so formed and the getter device. In addition, by connection of a cathode body, made of molybdenum and a shielding cylinder, made of tantalum, directly below the porous emission material carrier disk, a thermoelectric junction is created so that the thermo-voltage, produced at this point during operation, may be utilized for regulation of the emission temperature. For this purpose those portions of the mentioned parts representing the actual metal conductors, that is, storage container 3 and screening cylinder 4, are at least to a sufiiciently cold spot, made of the same respective metals. The thermo-voltage thus produced is, directly following appropriate amplification, conducted to the Wehnelt cylinder of the auxiliary discharge system, by means of which the emission temperature is determined, and thus automatically regulated through the discharge current intensity.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A beam producing system for an electron discharge device comprising, a storage metal capillary cathode having a storage container of cylindrical shape, a carrier disk mounted on one side of said storage container, a supply of emission substance in said storage container, an auxiliary electron discharge system mounted on the other side of said storage container and said auxiliary electron discharge system comprising a second storage container, a second carrier disk mounted on one side of said second storage container, and means for heating said second storage container to cause a beam of electrons to be discharged on to the other side of said first storage container.

2. A beam producing system according to claim 1 comprising a first metal foil cylinder attached to said first storage container and forming the support therefor and extending toward the auxiliary electron discharge system.

3. A beam producing system according to claim 2 comprising a second cylindrical foil mounted inside the first metal foil and formed with a plurality of apertured diaphragms for controlling the beam of the auxiliary electron discharge system.

4. A beam producing system according to claim 2 wherein said first metal foil cylinder is formed of tantalum.

5. A beam producing system according to claim 3 comprising a cylindrical control electrode in the form of a Wehnelt cylinder mounted adjacent the auxiliary electron discharge system to control the temperature of the storage metal capillary cathode.

6. A beam producing system according to claim 3 comprising a heat shield metal cylinder mounted about the first metal foil cylinder to improve the heat characteristics of said beam producing system.

7. A beam generating system for electric discharge vessels, particularly high frequency performance tu bes having a cathode emitting an electron beam which is heatable by direct electron impact, an auxiliary cathode mounted at a distance thereof from said cathode to provide for the necessary electron bombardment and the auxiliary cathode is mounted in the direction of the beam axis behind the cathode and designed as an indirectly heated storage cathode of the M-K-cathode type.

References Cited UNITED STATES PATENTS 11/1946 Kenyon 313-338 x 5/ 1950' Calbick 313-305 X 11/1961 Bailey et al. 313-338 X 4/1964 McHaney 313-337 5/1964 Merdinian 313-338 X 11/1965 Watson et al. 313-178 FOREIGN PATENTS 9/ 1950 Great Britain. 1/ 1957 Great Britain,

15 JOHN w. HUOKERT, Primary Examiner ANDREW J. JAMES, Assistant Examiner US. Cl. X.R. 

